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manuals=
manuals=
* [http://bama.edebris.com/download/tek/7904/Tektronix_7904_Service_May1983.pdf Tektronix 7904 Manual (PDF)]
* [http://bama.edebris.com/download/tek/7904/Tektronix_7904_Service_May1983.pdf Tektronix 7904 Manual (PDF)]
* [http://www.ko4bb.com/Manuals/Tektronix/Tektronix_-_7904A/7904a-service-1990.djvu Tektronix 7904A Manual (DjVu)]
* [http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=Tektronix/Tektronix_-_7904A Tektronix 7904A Manual (DjVu)]
* [http://w140.com/Tektronix_7904A_OCRed_by_Tabalabs.pdf Tektronix 7904A Manual (Shannon Hill PDF with OCR)]
* [http://w140.com/Tektronix_7904A_OCRed_by_Tabalabs.pdf Tektronix 7904A Manual (Shannon Hill PDF with OCR)]
* [http://w140.com/Tek_7904_OCRed_by_Tabalabs.pdf Tektronix 7904 Manual (Shannon Hill PDF with OCR)]
* [http://w140.com/Tek_7904_OCRed_by_Tabalabs.pdf Tektronix 7904 Manual (Shannon Hill PDF with OCR)]
* [http://w140.com/Tek_7904_Power_Supply.pdf Servicing the 7904 High-Efficiency Power Supply (PDF)]
* [http://w140.com/Tek_7904_Power_Supply.pdf Servicing the 7904 High-Efficiency Power Supply (PDF)]
<small>
'''Modifications'''
* [http://hakanh.com/dl/docs/kitinstructions/050-0650-00.pdf 050-0650-00 (1980) Vertical amplifier IC replacement]
* [http://hakanh.com/dl/docs/kitinstructions/050-0651-01.pdf 050-0651-01 (1975) Vertical output IC replacement (155-0065-00)]
* [http://hakanh.com/dl/docs/kitinstructions/050-0706-01.pdf 050-0706-01 (1980) Vertical output IC replacement (155-0065-00)]
* [http://hakanh.com/dl/docs/kitinstructions/050-0729-06.pdf 050-0729-06 (1980) A Trigger selector circuit board replacement]
* [http://hakanh.com/dl/docs/kitinstructions/050-0730-06.pdf 050-0730-06 (1980) B Trigger selector circuit board replacement]
* [http://hakanh.com/dl/docs/kitinstructions/050-0763-03.pdf 050-0763-03 (1981) Vertical interface circuit board replacement]
* [http://hakanh.com/dl/docs/kitinstructions/050-1014-00.pdf 050-1014-00 (1980) Vertical output IC replacement] ([[155-0064-00]])
* [http://hakanh.com/dl/docs/kitinstructions/050-1723-01.pdf 050-1723-01 (1983) P31 CRT replacement]
* [http://hakanh.com/dl/docs/custommods/7904mod721K.pdf Custom Mod 721K (1972) Single shot readout and/or grat illumination]
</small>
}}
}}
The '''Tektronix 7904''' is a 500 MHz, non-storage 7000-series oscilloscope mainframe with four bays. It accepts two [[7000-series_plug-ins#Vertical plug-ins|7000-series vertical plug-ins]] and two [[7000-series_plug-ins#Horizontal plug-ins|7000-series horizontal plug-ins]]. It was introduced in late 1971/early 1972 (Note 1). The successor model 7904A was introduced in 1974. There is also a rack-mount version, the [[R7903]], albeit with only one horizontal bay.
The '''Tektronix 7904''' is a 500 MHz, non-storage 7000-series oscilloscope mainframe with four bays.
It accepts two [[7000-series_plug-ins#Vertical plug-ins|7000-series vertical plug-ins]] and two [[7000-series_plug-ins#Horizontal plug-ins|7000-series horizontal plug-ins]].
It was introduced in late 1971/early 1972 (Note 1).
The successor model 7904A was introduced in 1984.
There is also a rack-mount version, the [[R7903]], albeit with only one horizontal bay.


Performance is largely determined by the plug-ins. The [[7A19]] vertical amplifier and [[7B92]] time base were introduced along with the 7904 to match the 500 MHz system bandwidth.   
Performance is largely determined by the plug-ins.
The [[7A19]] vertical amplifier and [[7B92]] time base were introduced along with the 7904 to match the 500 MHz system bandwidth.   


===7904A differences===
Design Staff of 7904 Project (from July 1971 Tekscope):
The 7904 had an elaborate 5-decade built-in calibrator with variable rate that was dropped from the 7904A.  In the 7904A, The Control Illumination switch moved to the rear panel, and the [[7000 series readout system|readout system]] gained a pulsed mode in which it is synchronized with the sweep instead of interrupting the display at random times.  This pulsed mode is not compatible with all time base plug-ins (see manual p. 1-12).
* [[Val Garuts]], project manager and horizontal and Z-axis amplifiers
* [[Thor Hallen]], vertical amplifier and [[7A19]]
* [[John McCormick]], horizontal amplifier
* [[Les Larson]] and [[Bill DeVey]], trigger and timebase ([[7B92]])
* [[Bill Peek]], Z-axis amplifier and autofocus
* [[Hans Springer]], mainframe interface and channel switching
* [[Joe Burger]], power supply
* [[Joel Swanno]], mechanical design
* [[Ken Hawken]], CRT


==Specifications==
{{BeginSpecs}}
{{BeginSpecs}}
{{Spec | Bandwidth | 500 MHz }}
{{Spec | Bandwidth | 500 MHz }}
{{Spec | Fastest calibrated sweep | 500 ps/Div (with [[7B92A]], other time bases "uncalibrated for first 60 ns") }}
{{Spec | Fastest calibrated sweep | 500 ps/Div (with [[7B92A]], other time bases "uncalibrated for first 60 ns") }}
{{Spec | Acceleration voltage | 24 kV }}
{{Spec | Acceleration voltage | 24 kV (+21 / -3 kV) }}
{{Spec | Calibrator (7904) | 4 mV, 40 mV, 400 mV, 4 V or 40 V (p-p) into 1 MΩ; 2 mV, 20 mV, 200 mV or 400 mV into 50 Ω; or 40 mA; selectable 1 kHz, ½ rep. rate of B Sweep Gate, or DC }}
{{Spec | Calibrator (7904) | 4 mV, 40 mV, 400 mV, 4 V or 40 V (p-p) into 1 MΩ; 2 mV, 20 mV, 200 mV or 400 mV into 50 Ω; or 40 mA; selectable 1 kHz, ½ rep. rate of B Sweep Gate, or DC }}
{{Spec | Calibrator (7904A) | 4 mV to 4 V (p-p) in decade steps, 1 kHz; 40 mV to 400 mV into 50 Ω }}
{{Spec | Calibrator (7904A) | 4 mV to 4 V (p-p) in decade steps, 1 kHz; 40 mV to 400 mV into 50 Ω }}
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}}
}}
{{EndSpecs}}
{{EndSpecs}}
===7904A differences===
The 7904A re-implements the vertical amplifier using Hypcon-packaged amplifier chips designed for the [[7104]], such as the [[155-0178-00]].
The 7904 had an elaborate 5-decade built-in calibrator with variable rate that was dropped from the 7904A. The [[7904 remote control connector|rear remote control connector]] unique to the 7904 was dropped as well.
In the 7904A, The Control Illumination switch moved to the rear panel, and the [[7000 series readout system|readout system]]
gained a pulsed mode in which it is synchronized with the sweep instead of interrupting the display at random times.
This pulsed mode is not compatible with all time base plug-ins (see manual p. 1-12).
===Options===
<div style="column-count:4;-moz-column-count:4;-webkit-column-count:4">
* Opt.2: X-Y delay compensation network
* Opt.3: Extra EMI shielding
* Opt.4: Maximum-brightness CRT with reduced area
* Opt.78: P11 phosphor
</div>


==Operation==
==Operation==


The 7904 has a many modes of operation. One mode is called "Independent-Pairs Display" in the manual, where the input to the left vertical plug-in is displayed using the B horizontal time-base plug-in, and the input to the right vertical plug-in is displayed using the A horizontal time-base plug-in. This resembles the trace-slaving "ALT" mode that is produced by an [[1A4]] in a [[547]]. Many other modes are available. It is possible to put vertical plug-ins in the horizontal slots for X-Y operation. It is even possible to put a horizontal plug-in in one of the vertical slots to produce a raster scan.   
The 7904 has many modes of operation.
One mode is called "Independent-Pairs Display" in the manual, where the input to the left vertical plug-in is displayed using the B horizontal time-base plug-in,
and the input to the right vertical plug-in is displayed using the A horizontal time-base plug-in.
This resembles the trace-slaving "ALT" mode that is produced by an [[1A4]] in a [[547]].
Many other modes are available.
It is possible to put vertical plug-ins in the horizontal slots for X-Y operation.
It is even possible to put a horizontal plug-in in one of the vertical slots to produce a raster scan.   


A special plug-in, the [[7A21N]], provides direct access to the deflection plates up to 1 GHz at an uncalibrated sensitivity of 4 V/Div. This plugin requires modifications to the mainframe to bypass the Y output amplifier (thus disabling readout and the other vertical plugin bay).
A special plug-in, the [[7A21N]], provides direct access to the deflection plates up to 1 GHz at an uncalibrated sensitivity of 4 V/Div.
This plugin requires modifications to the mainframe to bypass the Y output amplifier (thus disabling readout and the other vertical plugin bay).
 
A rear-panel [[7904 remote control connector| remote control connector]] has connections for single-sweep ready lamps, a reset button, and readout control.


==Internals==
==Internals==
The 7904 uses a switch-mode power supply and has no fan. It incorporates a 65 ns Y delay line. This delay is too short for some older time bases such as [[7B53]] to display the trigger event.
The 7904 uses a switch-mode power supply and has no fan. It incorporates a 65 ns Y delay line.
This delay is too short for some older time bases such as [[7B53]] to display the trigger event.


The 7904 makes extensive use of custom integrated circuits and hybrid circuits, inter alia, the [[155-0064-00]] 470-ps output amplifier, [[155-0022-00]] analog multiplexer for channel switching, [[155-0059-00]] HF amplifier, [[155-0095-01]] and [[155-0095-03]] differential HF amplifiers, and [[155-0067-02]] SMPS controller.
[[Thor Hallen]] designed the main vertical amplifier and the [[7A19]] plugin (Note 1).
It used bridged T coils and the "[[ft doubler|f<sub>t</sub> doubler]]" circuit patented by [[Carl Battjes]] to achieve its bandwidth.


The signal path is completely differential and all of the internal wiring is 50 Ω coax. The CRT ([[154-0644-05]]) has distributed vertical deflection plates.
The 7904 makes extensive use of custom integrated circuits and hybrid circuits, inter alia, the [[155-0064-00]] 470-ps output amplifier,
[[155-0022-00]] analog multiplexer for channel switching, [[155-0059-00]] HF amplifier,
[[155-0095-01]] and [[155-0095-03]] differential HF amplifiers, and [[155-0067-02]] SMPS controller. 
 
The 7904A includes [[155-0173-05]], [[155-0175-05]] and [[155-0178-05]] amplifiers.
 
The signal path is completely differential and the internal signal wiring is 50 Ω coax.
The CRT ([[154-0644-05]]) has [[distributed vertical deflection plates]].


==Prices==
==Prices==
1990: $12,750 (7904A) = $23,200 @ 2014 value
{| class="wikitable"
|-
! &nbsp;
! Year
! 1972
! 1976
! 1980
! 1984
! 1990
|-
! Model
|
|align=center| 7904
|align=center| 7904
|align=center| 7904
|align=center| 7904A
|align=center| 7904A
|-
!rowspan=2| Mainframe only
! Catalog price
|align=right|  $2,900
|align=right|  $4,100
|align=right|  $6,265
|align=right|  $8,810
|align=right| $12,750
|-
! 2019 value
|align=right| $17,640
|align=right| $18,320
|align=right| $19,330
|align=right| $21,550
|align=right| $24,800
|-
!rowspan=2| Mainframe with [[7A19]],<br />7A19 Opt. 04, [[7B92]]
! Catalog price
|align=right|  $5,500
|align=right|  $7,765
|align=right| $12,015
|align=right| $17,425
|align=right| $24,190
|-
! 2019 value
|align=right| $33,450
|align=right| $34,690
|align=right| $37,070
|align=right| $42,630
|align=right| $47,050
|}


==Links==
==Links==


* [http://amplifier.cd/Test_Equipment/Tektronix/Tektronix_7000_series_mainframe/7904.htm Tek 7904 page at amplifier.cd]
* [https://lazyelectrons.wordpress.com/2018/11/24/tektronix-7904-oscilloscope-power-supply-repair/ 7904 Repair with Video]
* [http://amplifier.cd/Test_Equipment/Tektronix/Tektronix_7000_series_mainframe/7904A.htm Tek 7904A page at amplifier.cd]
* [[Media:Tekscope 1971 V3 N4 Jul 1971.pdf | Tekscope Vol. 3 No. 4, Jul 1971]]
* [http://amplifier.cd/Test_Equipment/Tektronix/Tektronix_7000_series_mainframe/7904.htm Tek 7904] / [http://amplifier.cd/Test_Equipment/Tektronix/Tektronix_7000_series_mainframe/7904A.htm 7904A] @ amplifier.cd
* [http://www.barrytech.com/tektronix/tek7000/tek7904.html Tek 7904] / [http://www.barrytech.com/tektronix/tek7000/tek7904a.html 7904A] @ barrytech.com
* [https://www.circuitsathome.com/measurements/repairing-front-panel-buttons-of-tektronix-7904-oscilloscope Repairing front panel buttons of Tektronix 7904 oscilloscope]
* [https://www.circuitsathome.com/measurements/repairing-front-panel-buttons-of-tektronix-7904-oscilloscope Repairing front panel buttons of Tektronix 7904 oscilloscope]
* [http://www.ko4bb.com/Manuals/Tektronix/Tektronix_-_7904A/Tek_7904_Power_Supply.pdf Servicing the 7904 high-efficiency power supply (Tektronix ServiceScope article)]


==Notes==
==Notes==
# See [[7A11]] and [[John Addis]], ''Good Engineering and Fast Vertical Amplifiers'', in Jim Williams (Ed.), ''Analog Circuit Design: Art, Science and Personalities'' (1991), p.114, and [http://w140.com/tektronix_new_products_1972.pdf Tektronix New Products 1972] brochure.
# See [[7A11]] and [[John Addis]], ''Good Engineering and Fast Vertical Amplifiers'', in [[Jim Williams]] (Ed.), ''Analog Circuit Design: Art, Science and Personalities'' (1991), p.114, and [http://w140.com/tektronix_new_products_1972.pdf Tektronix New Products 1972] brochure.
   
   
==Pictures==
==Pictures==
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===7904 non-A===
===7904 non-A===
<gallery>
<gallery>
File:Tek-7904-front.jpg | 7904  (non-A) front
Tek-7904-front.jpg | 7904  (non-A) front
File:7904-left.jpg | Left side. Left top: Vertical amplifier; left bottom: switch-mode power supply; right center: delay line; right bottom: plug-in bays
Tek 7904 rear.jpg | 7904 rear
File:7904-right.jpg | Right side.  Top left: calibrator; bottom left: plug-in bays; top center: [[7000 series readout system|readout board]];  top right: Z amplifier  
7904-left.jpg | Left side. Left top: Vertical amplifier; left bottom: switch-mode power supply; right center: delay line; right bottom: plug-in bays
File:7904-right-front.jpg | Right side detail. Left: calibrator; right: readout.
7904-right.jpg | Right side.  Top left: calibrator; bottom left: plug-in bays; top center: [[7000 series readout system|readout board]];  top right: Z amplifier  
File:7904 interface 1.jpg|Plug-in interface board front (left piggyback board removed)
7904-right-front.jpg | Right side detail. Left: calibrator; right: readout.
File:7904 interface 2.jpg|Plug-in interface board rear
7904 interface 1.jpg|Plug-in backplane board front (left trigger selector piggyback board removed)
File:7904-x-amp.jpg | Horizontal (X) amplifier board
Tek7904-trig-selector.jpg | B Trigger selector piggyback board (A6)
File:7904-y-amp.jpg | Vertical (Y) amplifier board
Tek7904-vertical-interface.jpg | Vertical interface piggyback board (A7).  The two [[155-0095-03]] amplifiers (large metal cans) are used to select the signal from one vertical plug-in bay, and drive the delay line.
File:7904-z-amp.jpg | Z amplifier board
7904 interface 2.jpg|Plug-in backplane board rear
File:7904-controls.jpg | front-panel controls
Tek7904-backplane-bottom.jpg | Backplane board sandwich seen from below
File:7904_block.gif|7904 block diagram
7904-x-amp.jpg | Horizontal (X) amplifier board
7904-y-amp.jpg | Vertical (Y) amplifier board
7904-z-amp.jpg | Z amplifier board
7904-controls.jpg | front-panel controls
7904_block.gif|7904 block diagram
Tek7904-7a19-7b92a-1010mhz-hfsync.jpg | A 7B92A (B098xxx) displaying a 1.01 GHz sine in HF Sync mode ([[7904]] mainframe, [[7A19]] amplifier).
 
</gallery>
====Power Supply====
<gallery>
7904-psu-internal.jpg    | 7904 switchmode power supply, covers removed
7904-psu-right.jpg        | View from right (as seen from front of instrument)
7904-psu-primary.jpg      | Primary side circuit board
7904-psu-primary-caps.jpg | Primary side capacitors
7904-psu-transformer.jpg  | Detail view of transformer from the side
7904-psu-rectifier.jpg    | Secondary side rectifier board
7904-psu-regulator.jpg    | Secondary side post-regulator
</gallery>
</gallery>
===7904A===
===7904A===
<gallery>
<gallery>
File:7904A_1.JPG|7904A
7904a-front.jpg |7904A
7904A_rear.jpg |7904A Rear
7904A_top1.jpg |7904A Top with Horizontal Amplifier at top right
7904A_right1.jpg |7904A Right with Z-axis on top right and 2nd Gen. Readout board at bottom right
7904A_left1.jpg |7904A Left with Vertical Amplifier (top) and Vertical switch board (bottom)
7904A_topleft1.jpg |7904A Topleft
7904A_left_closeup.jpg |7904A Closeup of Vertical amplifier
7904a lvps1.png|7904A Low-voltage Power Supply Schematic
7904a-h-v.jpg | 7904A Horizontal and vertical amplifiers
</gallery>
</gallery>




[[Category:7000 series non-storage mainframes]]
[[Category:7000 series non-storage mainframes]]
__NOTOC__
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